CMakeLists.txt: Removed force to -march=native
CMakeLists.txt: Removed force to -march=native

Setting the arch to native for arm.* should not generally be necessary.
If this is absolutely required, it can be passed manually.  Setting
-march=native seems to fail on some versions of gnu gcc for arm.
Removed the force to -march=native in favor of letting cmake set the
arch.

If at some point, this would be required, a better way would be to add
the compile flag after testing if it is supported.

Example:
    upm_add_compile_flags(CXX "-march=native")

Signed-off-by: Noel Eck <1e36ab6ededef40f3f16bdbc1b09eee72c5d08cf@intel.com>

pylbert/upm,skiselev/upm,jontrulson/upm,Jon-ICS/upm,g-vidal/upm,skiselev/upm,g-vidal/upm,jontrulson/upm,jontrulson/upm,skiselev/upm,intel-iot-devkit/upm,stefan-andritoiu/upm,intel-iot-devkit/upm,intel-iot-devkit/upm,sasmita/upm,skiselev/upm,stefan-andritoiu/upm,Jon-ICS/upm,Jon-ICS/upm,intel-iot-devkit/upm,pylbert/upm,Propanu/upm,stefan-andritoiu/upm,malikabhi05/upm,Jon-ICS/upm,sasmita/upm,sasmita/upm,malikabhi05/upm,stefan-andritoiu/upm,intel-iot-devkit/upm,sasmita/upm,g-vidal/upm,Propanu/upm,Propanu/upm,malikabhi05/upm,g-vidal/upm,sasmita/upm,malikabhi05/upm,malikabhi05/upm,stefan-andritoiu/upm,pylbert/upm,Propanu/upm,skiselev/upm,g-vidal/upm,jontrulson/upm,pylbert/upm,Propanu/upm,intel-iot-devkit/upm,malikabhi05/upm,pylbert/upm,skiselev/upm,Jon-ICS/upm,g-vidal/upm,pylbert/upm,stefan-andritoiu/upm,jontrulson/upm,Propanu/upm